¹Pharmaceutical Clinical Research Center, Yamaguchi University Hospital, Ube, Yamaguchi, Japan; Department of Cardiovascular Medicine, Yamaguchi University Graduate School of Medicine, Ube, Yamaguchi, Japan.

Abstract

Recent studies have suggested that the calcium antagonists have an antiatherogenic antioxidant property. The effects of the calcium antagonists on reactive oxygen species (ROS)-related enzymes, however, remain unknown. We hypothesized that the calcium antagonists inhibit oxidative stress in the heart of stroke-prone hypertensive rats (SHRSPs) through superoxide dismutase (SOD). Male 12-week-old Wister-Kyoto rats (WKY) and SHRSPs were treated for 6 weeks with a vehicle, amlodipine (5 mg/kg/day), or enalapril (10 mg/kg/day). NAD(P)H oxidase activity was measured by a luminescence assay. SOD activity was measured spectrophotometrically. Protein expressions were analyzed by immunoblots. Systolic blood pressure (SBP) in the vehicle SHRSP group was significantly higher than that in the WKY group. Both drugs significantly and equally reduced SBP compared to the vehicle SHRSP group. However, both drugs showed significantly higher SBP than the WKY group. Both drugs showed equipotent effects on left ventricular hypertrophy and fibrosis, the wall-to-lumen ratio, manganese SOD, ROS assessed by both 8-isoprostane and thiobarbituric acid reactive substances, and eNOS in the SHRSP hearts. NAD(P)H oxidase activity was significantly upregulated in the vehicle SHRSP group compared with those values in the WKY group. There was a significant reduction in NAD(P)H oxidase activity in the enalapril group almost to the same levels as those of the WKY group. In contrast, amlodipine reduced NAD(P)H oxidase activity in SHRSP heart compared with those in the vehicle SHRSP group, however, the levels of NAD(P)H oxidase activity in the amlodipine group were still significantly higher than those of the WKY group. Inversely, Cu/ZnSOD expression and activity were significantly downregulated in the vehicle SHRSP group compared with those values in the WKY group. Compared to the vehicle SHRSP group, Cu/ZnSOD expression and activity in the SHRSP heart were significantly upregulated in both drug-treated groups, and only the amlodipine group restored Cu/ZnSOD expression and activity to the same levels as those of the WKY group. Thus, amlodipine might inhibit oxidative stress in the SHRSP heart by efficiently restoring Cu/ZnSOD activity, suggesting that the calcium antagonist may have antiatherogenic antioxidant action by selectively restoring Cu/ZnSOD activity in hypertension.